Method of operating a wind power installation and a wind power installation

ABSTRACT

The present invention concerns a method of operating a wind power installation comprising an electric generator drivable by a rotor for outputting electrical power to an electrical consumer, in particular an electrical network. 
     The invention further concerns a wind power installation comprising a rotor and an electric gererator coupled to the rotor for outputting electric power to an electrical consumer, in particular an electrical network. 
     The object of the present invention is to provide a method of operating a wind power installation, and a wind power installation, which avoid the disadvantages of the state of the art and in particular avoid voltage over-fluctuations at the consumer, in particular an electrical network, and unwanted shut-down of the wind power installation. 
     In a method of the kind set forth in the opening part of this specification, that object is attained by the invention in that the power delivered to the network by the wind power generator is regulated in dependence on the applied network voltage of the power supply network.

BACKGROUND OF THE INVENTION

The present invention concerns a method of operating a wind powerinstallation comprising an electric generator drivable by a rotor foroutputting electrical power to an electrical consumer, in particular anelectrical network.

The invention further concerns a wind power installation comprising arotor and an electric generator coupled to the rotor for outputtingelectric power to an electrical consumer, in particular an electricalnetwork.

In the known wind power installations for generating electrical energyfrom wind the generator is operated in parallel relationship with theelectrical consumer, frequently an electrical network. During operationof the wind power installation the electric power produced by thegenerator varies in dependence on the prevailing wind speed and thus thewired power. The consequence of this is that the electrical generatorvoltage is also variable in dependence on the wind power. That givesrise to the following problems:

In the event of the electrical power generated being fed into anelectrical network, for example a public power supply network, there isan increase in the network voltage at a connecting point or networkjunction point at which the electrical generator power is fed into thenetwork. Particularly in the event of severe changes in the generatorvoltage, There are severe unwanted changes in the network voltage.

Under particular circumstances it can happen that the network voltage inthe supply network rises to an undesirably high value. That is the casein particular when the power taken on the part of the consumers is verylow while a high level of electrical power is being fed into the supplynetwork. Such situations can occur for example at night when theelectrical consumption in households is fairly low while with a strongwind, a wind power converter provides the power supply network with acorrespondingly high level of electrical power. If the voltage in thesupply network or at the network connection point of the wind powerinstallation rises above a predetermined value, the wind powerinstallation or the generator thereof has to be disconnected from thenetwork and the wind power installation would have to be completely shutdown from the network because it is no longer possible to take anypower. A shut-down procedure of that kind results in an interruption inthe feed of electrical power, which is unwanted equally From the pointof view of the operator of the wind power installation and the operatorof the network.

It is generally known from German patent specification No 368 799, DE-OSNo 44 28 085 and DE-OS No 30 23 195 that, in installations such as windpower installations or solar generators, the power produced by thegenerator fluctuates, which gives rise to the above-described problemsin terms of the feed of power into the network.

OBJECTS AND SUMMARY OF THE INVENTION

The object of the present invention is to provide a method of operatinga wind power installation, and a wind power installation, which avoidthe disadvantages of the state of the art and in particular avoidvoltage over-fluctuations at the consumer, in particular an electricalnetwork, and unwanted shut-down of the wind power installation.

In a method of the kind set forth in the opening part of thisspecification, that object is attained by the invention in that thepower supplied to the network by the wind power generator is regulatedin dependence on the applied network voltage of the power supplynetwork.

In an apparatus of the kind set forth in the opening part of thisspecification, the object of the invention is attained by a regulatingdevice having a voltage sensor for sensing an electrical voltage appliedat the consumer, for example network voltage, so that the power suppliedto the consumer by the generator can be regulated in dependence on thevoltage sensed by the voltage sensor.

As described, in the case of energy generation, there can be afluctuation in the energy which can be generatec, which in the case ofwind power installations is governed by natural conditions in dependenceon wind strength. Those fluctuations however are not the basic startingpoint of the invention. On the contrary, the invention is concerned withthe problem that fluctuations in power consumption also occur on theconsumer side, which has an effect in the form of a fluctuating networkvoltage. It is known that such network voltages are critical becauseelectrical equipment—in particular computers—are frequently onlyinadequately safeguarded against critical voltage fluctuations. Theinvention therefore provides that not just the fluctuation in energygeneration on the generator side but also the fluctuation on theconsumer side is taken into consideration in regard to the feed ofenergy into the system so that the electrical voltage produced isregulated at the feed-in point to the desired reference value.

The invention avoids unwanted fluctuations in the voltage apolied at theconsumer, in particular the electrical voltage in a network, insofar asthe electrical power delivered by the generator is regulated independence on the voltage of the consumer or the network. That alsoavoids unwanted voltage fluctuations which can arise out of changes inwind power.

A further advantage of the invention is that, even with very substantialchanges in wind power, the wind power installation does not need to beshut down in order to avoid fluctuations in the network system. Inaccordance with the invention, even with considerable changes in windpower, the wind power installation continues to be operated withoutchanges in network voltage occurring. For that purpose the regulatingdevice according to the invention is equipped with voltage sensors forsensing the voltage at the consumer or the network.

In addition, with a constant wind power, it is possible by means of theinvention to compensate for network fluctuations as regularly occur inelectrical networks for energy power supply as some consumers connectedto the network from time to time draw large amounts of power from thenetwork, and that can result in a reduction in voltage. In the case ofsuch a reduction in voltage the wind power installation according to theinvention can feed an increased amount of electrical power into thenetwork and in that way it can compensate for voltage fluctuations. Forthat purpose the feed-in voltage is raised at the interface between thewind power installation and the network, for example on the basis of thenetwork voltage value which is sensed in accordance with the invention.

In accordance with a preferred embodiment of the method according to theinvention the power supplied is regulated by the electrical voltageproduced being regulated to a desired reference value. In this casenetwork voltage compensation can be implemented in a particularly simplemanner, which—as described hereinbefore—can occur when a consumerconnected to the network requires a large amount of power.

In accordance with a further preferred embodiment of the invention theelectrical voltage is produced in the form of ac voltage at apredeterminable frequency. In that way the power fed into the system canbe adapted to the conditions in the network and the network frequencycan be influenced thereby. The predeterminable frequency desirablycorresponds to the network frequency.

A further development of the wind power installation according to theinvention advantageously involves a regulating device having amicroprocessor as digital regulation can be implemented in that way.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described hereinafter by means of an embodiment of amethod of operating a wind power installation with reference to thedrawings in which:

FIG. 1 is a diagrammatic view of a wind power installation which feedsinto a network,

FIG. 2 shows a regulating device according to the invention for theoperation of a wind power installation, and

FIG. 3 is a diagram showing the relationship between wind power andnetwork or mains voltage.

DETAILED DESCRIPTION OF THE INVENTION

A wind power installation 2 diagrammatically illustrated in FIG. 1 andhaving a rotor 4 is connected to an electrical network 6 which forexample can be a public network. Connected to the network are aplurality of electrical consumers 8.

The electric generator (not shown in FIG. 1) of the wind powerinstallation 2 is coupled to an electrical control and regulatingarrangement 10 which firstly rectifies the alternating current generatedin the generator and then converts it into an ac voltage whichcorresponds to the network frequency. Instead of a network 6, it wouldalso be possible to supply electrical energy to an individual consumerfrom the wind power installation 2. The control and regulatingarrangement 10 has a regulating device according to the invention.

FIG. 2 shows the regulating device according to the invention. Thediagrammatically illustrated rotor 4 is coupled to a generator 12producing electrical power which depends on the wind speed and thus thewind power. The ac voltage generated in the generator 12 can firstly berectified and then converted into an ac voltage which is of a frequencycorresponding to the network frequency as illustrated in FIG. 4.

The network voltage is ascertained at a location in the network 6(FIG. 1) by means of a voltage sensor (not shown). An optimum generatorvoltage U_(ref) (see FIG. 2) is calculated in dependence on theascertained network voltage, possibly means of a microprocessor which isshown in FIG. 4 and a voltage sensor U. The generator voltage U_(actual)from sensor U is then regulated to the desired voltage value U_(ref) bymeans of the regulating device including PDI controller C. Thatregulation of the generator voltage provides for regulation of theelectrical power which is delivered by the generator 12 to a consumer,in the illustrated embodiment being the network 6, and which is fed intothe network 6, and which is fed into the network 6. By virtue of thisfeedback scheme, into the network, fluctuations in the network voltagein the network 6 can be avoided or considerably reduced.

The diagram illustrated in FIG. 3 shows th relationship between thepower WP which is entered on the ordinate and which is delivered by thewind power installation and the network voltage G which is plotted onthe abscissa. If the network voltage differs only little from itsreference value which is between the voltage values U_(min) and U_(max)then a uniform level of power WØ is delivered to the network by thegenerator, corresponding to the upper straight portion of the curve(straight line parallel to the abscissa). If the network voltage risesfurther and exceeds a value U1 at point P1, the power fed into thenetwork is reduced. When the value U_(max) is reached, then the power WPfed into the network is equal to zero )point P2). Even in the case wherethere is a high level of wind power, no power is fed into the network atpoint P2. If the wind power falls sharply, then only a reduced amount ofpower can still be fed into the network. Even if no further power isdelivered on the part of the wind power converted, the latter—althoughwithout delivering power—continues to be operated so that power deliverycan always be effected as soon as the mains voltage has again assumed avalue between U_(min) and U_(max). As shown in FIG. 3 the power PW isalso increased from O to WØ as the network voltage G increases fromU_(min) to U₃.

FIG. 4 shows essential components of the control and regulatingarrangement 10 in FIG. 1. The control and regulating arrangement 10 hasa rectifier 16 in which the ac voltage produced in the generator isrectified. A frequency converter 18 connected to the rectifier 16converts the initially rectified dc voltage into an ac voltage which isfed into the network 6 by way of the lines L1, L2 and L3, in the form ofa three-phase ac voltage. The frequency converter 18 is controlled bymeans of a microcomputer 20 which is part of the overall regulatingdevice. For that purpose the microprocessor 20 is coupled to thefrequency converter 18. The input parameters for regulation of thevoltage with which the electrical power afforded by the wind powerinstallation 2 is fed into the network 6 are derived from sensors S andinclude the current network voltage G, the network frequency f, theelectrical power PW of the generator, the reactive power factor cos φand the power gradient dP/dt. Regulation in accordance with theinvention of the voltage to be fed into the network is implemented inthe microprocessor 20.

FIG. 5 shows the variation in respect of time of the voltages andcurrents of the three phases of the network 6.

What is claimed is:
 1. A method of operating a wind power installationincluding an electrical generator driven by a rotor for supplyingelectrical power to an electrical network having a network voltage andbeing connected to a customer, comprising: sensing said network voltage;supplying electrical power to the electrical network at a supplied powerlevel in accordance with said network voltage; and reducing saidsupplied power level to a lower level when said network voltage exceedsa threshold value U1.
 2. The method of claim 1 wherein said generator iscapable of generating said electrical power at a nominal power leveldependant on current wind conditions, wherein said lower level is lowerthan said nominal power level.
 3. The method of claim 1 wherein saidstep of reducing said supplied power level includes reducing saidsupplied power level gradually as said network voltage increases abovesaid threshold U1.
 4. The method of claim 3 wherein said step ofreducing said supplied power level includes reducing said electricalpower level to a zero level when said network voltage reaches athreshold value Umax.
 5. The method of claim 4 wherein said step ofreducing further comprises maintaining said supplied power level at saidzero level as said network voltage rises above said threshold levelU_(max).
 6. The method of claim 3 wherein said step of reducing saidelectrical power includes reducing said electrical power linearly assaid network voltage increases between U1 and U_(max).
 7. The method ofclaim 1 wherein said sensing includes sensing said network voltage atthe point at which said electrical power is fed to said electricalnetwork.
 8. The method of claim 1 further generating said electricalpower at a predeterminable frequency.
 9. The method of claim 8 whereinsaid electrical network is operating at a network frequency, whereinpredeterminable frequency corresponds substantially to said networkfrequency.
 10. A wind power installation for delivering electrical powerto an electrical network comprising: a rotor rotated by wind; anelectrical generator coupled to said rotor and adapted to supplyelectrical power at a supplied power level to the electrical network;and a regulating device having a voltage sensor for sensing a networkvoltage associated with the electrical network, said regulating devicebeing coupled to said electrical generator to control said power levelin accordance with said network voltage, wherein said regulating deviceis adapted to reduce said supplied power level when said network voltageexceeds a level U1.
 11. The wind power installation as set forth inclaim 10 wherein said regulating device has a microprocessor.
 12. Thewind power installation as set forth in claim 10 wherein said regulatingdevice is adapted to reduce said supplied power level from a firstthreshold to a second threshold level as said network voltage increasesfrom level U1 to a level U_(max).
 13. The wind power installation as setforth in claim 12 wherein said regulating device is adapted to reducesaid supplied power level from said first to said second threshold levellinearly.
 14. The wind power installation of as set forth in claim 13wherein said second threshold level is zero.
 15. A method of operatingan energy-generating apparatus including an electric generator forsupplying electrical power to an electrical network, the electricalnetwork being connected to at least one consumer and having a networkvoltage that fluctuates with demand, said method comprising: supplyingelectrical power from said electrical generator to said electricalnetwork at a supplied power level; and regulating said supplied powerlevel to protect said network from over-voltage by reducing saidsupplied power level when said network voltage exceeds a value U1. 16.The method as set forth in claim 15 wherein said supplied power level isregulated by reducing said supplied power level to a zero level as saidnetwork voltage increases from said value U1 to a value U_(max).
 17. Themethod as set forth in claim 16 wherein said supplied power level isreduced linearly.
 18. The method as set forth in claim 16 wherein saidsupplied power level is maintained at a threshold level as set networkvoltage increases above said value Umax.
 19. The method as set forth inclaim 18 wherein said threshold level is zero.
 20. The method of claim15 further comprising increasing said supplied power level as saidnetwork voltage increases from a level U_(min) to a level U3, saidlevels U_(min) and U3 being smaller than said level U1.
 21. The methodof claim 15 wherein said supplied power level is maintained constantwhen said network voltage is below said level U1.
 22. The method ofclaim 15 wherein said supplied power level is maintained constant whensaid network voltage is between a level U3 and U1, U3 being lower thanU1.